BURNUP CREDIT USING ACTINIDES ONLY FOR PWR SPENT NUCLEAR FUEL PACKAGES

The methodology submitted on May 31, 1995, to the NRC for performing and applying nuclear criticality safety calculations, for PWR spent nuclear fuel (SNF) packages with actinide-only burnup credit, is briefly described. The changes in the U-234, U-235, U-236, U-238, Pu-238, Pu-239, Pu-240, Pu- 241, Pu-242, and Am-241 concentration with bumup are used in bumup credit criticality analyses. No credit for fission product neutron absorbers is taken. The methodology consists of five major steps. 1) Validate a computer code system to calculate isotopic concentrations of SNF created during burnup in the reactor core and subsequent decay. 2) Validate a computer code system to predict the subcritical multiplication factor, keff, of a spent nuclear fuel package. 3) Establish bounding conditions for the isotopic concentration and criticality calculations. 4) Use the validated codes and bounding conditions to generate loading criteria (burnup credit loading curves). 5) Verify that SNF assemblies meet the package loading criteria and confirm proper assembly selection prior to loading. Each step is described for use with any computer code system. The method is demonstrated with the SCALE 4.2 computer code package using 27BURNUPLIB cross sections.